body {
    font-family: 'Helvetica Neue', Arial, 'Hiragino Kaku Gothic ProN', 'Hiragino Sans', Meiryo, sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    background-color: #f0f2f5;
}

.container {
    background-color: white;
    padding: 2rem;
    border-radius: 1rem;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    text-align: center;
    width: 300px;
}

h1 {
    color: #333;
    margin-bottom: 1.5rem;
    font-size: 1.5rem;
}

.timer-display {
    font-size: 4rem;
    font-weight: bold;
    color: #2c3e50;
    margin: 1rem 0;
    font-feature-settings: "tnum";
    font-variant-numeric: tabular-nums;
}

.input-group {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 0.5rem;
    margin-bottom: 1.5rem;
}

input[type="number"] {
    width: 60px;
    padding: 0.5rem;
    border: 1px solid #ccc;
    border-radius: 4px;
    font-size: 1rem;
    text-align: center;
}

.controls {
    display: flex;
    justify-content: space-between;
    gap: 0.5rem;
}

button {
    flex: 1;
    padding: 0.75rem;
    border: none;
    border-radius: 4px;
    font-size: 1rem;
    cursor: pointer;
    transition: background-color 0.2s;
    font-weight: bold;
}

#startBtn {
    background-color: #4CAF50;
    color: white;
}

#startBtn:hover:not(:disabled) {
    background-color: #45a049;
}

#stopBtn {
    background-color: #f44336;
    color: white;
}

#stopBtn:hover:not(:disabled) {
    background-color: #da190b;
}

#resetBtn {
    background-color: #9e9e9e;
    color: white;
}

#resetBtn:hover:not(:disabled) {
    background-color: #757575;
}

button:disabled {
    background-color: #cccccc;
    cursor: not-allowed;
    opacity: 0.7;
}